This invention relates to a swimming fin or flipper used during swimming.
Japanese Utility Model Application Disclosure Gazette (Kokai) No. Hei5-63563 discloses a swimming fin formed on a top surface of a blade with a plurality of grooves to obtain a high thrust during down-kicking movement of the swimming fin. Such a blade is transversely curved with the top surface thereof inside during the down-kicking movement so that an amount of water caught inside the blade may be moved backward of a swimmer and thereby a high thrust may be obtained. The presence of the grooves is claimed to facilitate the blade to be curved.
With this known swimming fin, the grooves formed on the top surface of the blade form the corresponding ribs on a bottom surface of the blade. These ribs make it difficult to deform the swimming fin smoothly during up-kicking movement of the swimming fin and to alleviate a water resistance. Consequently, if the swimmer intends to obtain a high thrust by the down-kicking movement of the swimming fin, a physical burden imposed on the swimmer is increased and inevitably the up-kicking movement of the swimming fin becomes slow.